The molecular mechanisms involved in the developmental regulation of gene activity will be studied in sea urchin embryos. Sequences of mRNA molecules that are developmentally regulated will be cloned in bacterial plasmids and used for a number of approaches to elucidate parameters of regulation. Hybrid selection of nuclear precursors and of mRNA from in vitro labeled RNA populations will be carried out to measure the rate of transcription, processing and decay of individual regulated sequences. Hybrid selected mRNA will be translated in vitro to determine the protein product of the developmentally regulated genes. The recombinant plasmids with mRNA sequences will be used to select the genomic oodemia sequences from a library of genomic DNA. The methylation of organization in chromatic structures of such genomic sequences will be examined at various developmental stages to determine how these change when the fate of cells is determined in early sea urchin embryogenis and when gene transcription is activated at what is now thought to be a later time. Three types of sequences will be cloned and studied in this way: Ribosomal RNA genes which are most active in oocytes and extensively repressed in embryos, oocyte/cleavage specific mRNA that are moderately abundant in eggs and cleavage stages but reduced in pluteni, and pluteus-specific mRNA that are abundant in gastrula and plateus cells but not in blastula cells.